This invention relates to a spindle which when heated by means of an electric heating coil expands to fit a mating toolholder. The spindle is then cooled by means of a refrigerant blast and contracts to grip the toolholder having an extremely beneficial effect on the rigidity and concentricity of the toolholder. One of the problems this invention solves is working with shrink fit chucking devices, it is often difficult to remove a tool from the chuck since heating the chuck causes the tool to be heated by conduction as well. This problem is solved by a refrigerant blast through the air lines capable of receiving a refrigerant blast provided in the toolholder also the toolholder is manufactured from a predetermined type of steel with a lower thermal expansion rate than that of the internal diameter of the spindle bore.
This prevents the toolholder from being heated by conduction at the same rate as the internal diameter of the spindle bore thus making for easy removal of the said toolholder.
Another problem this invention solves is an extremely accurate spindle is needed for use in modern day machine tools which employ the use of automatic toolchanger arms. Also an extremely accurate spindle is needed anywhere high-speed machining is prevalent. New and improved spindles for high-speed machining are always needed in the automotive and aerospace industries. Although the related prior art Erickson et al. U.S. Pat. No. 4,747,735; Erickson U.S. Pat. No. 4,723,877; Massa U.S. Pat. No. 5,127,780 have good accuracy and work holding capabilities they are toolholders. One problem with toolholders is they are used in conventional spindles which do not employ shrink fit technology therefore they have limited rigidity and concentricity capabilities. These toolholders are extended out from the spindle which can often magnify the poor rigidity and concentricity of the spindle being used to hold these toolholders.
Various types of spindles are known for locating tools in a rigid manner. The Kramer et al. U.S. Pat. No. 5,277,435 holds a tool that is shrink fit into a spindle.
Some of the problems with this are the tool that goes into the spindle is not symmetric making concentricity and rigidity suspect where high-speed machining applications are concerned also it can not be adapted to fit a machine tool with an automatic tool changer arm and no mention is made of this in the specification and claims of the said patent.
The Marquart U.S. Pat. No. 5,280,671 shows a collet chuck that employs shrink fit technology. Some of the problems with this invention are the use of a collet chuck for a clamping device that is fastened to the spindle by a clamping apparatus, which makes for suspect rigidity and concentricity. Another significant drawback is that it can be difficult to remove the tool from the chuck since heating the chuck causes the tool to be heated by conduction as well. Moreover relatively high temperatures are needed in order to effect sufficient expansion of the chuck to remove the tool. Also the said invention can not be adapted to fit a machine tool with an automatic toolchanger arm efficiently because there is no way of cooling the tool to be removed and no mention is made of this in the specification or claims of the said invention.